1. Field of the Invention
This invention relates to polyisocyanurate polymers and is more particularly concerned with improved polyisocyanurate foams, films, coatings, and the like.
2. Description of the Prior Art
The trimerization of an excess of organic polyisocyanates with minor amounts of polyhydric alcohols to form polyisocyanurate-polyurethane polymers is well known in the art; see for example U.S. Pat. Nos. 3,745,133, 3,986,991, 3,896,052, and 3,899,443.
When the faster polyurethane forming reaction is combined in the same formation with the slower polyisocyanurate reaction, various types of problems can occur. The prior art has dealt with this problem of unequal reactivity mainly by employing particular catalysts or catalyst combinations for particular tasks; see particularly the last three patents cited supra.
The prior art still suffers from the difficulty of slow overall cure rate at the finish of the polymer forming reaction. If sufficient amounts of catalyst are employed to effect rapid cure a too rapid onset of the polymerization process occurs making handling of the material difficult if not impossible.
It has now been discovered that the trimerization of polyisocyanates in the presence of a minor amount of a carbamate modifier provides polyisocyanurate polymers which have a much more rapid and deeper cure than prior art materials and yet, at the same time, have the same or slower initiation rates.
The carbamate modifiers, because they have no hydroxyl groups to form polyurethanes, allow the presence of catalyst levels, which, surprisingly, can be ten to twenty times the amounts used in conventional trimer/urethane reactions. The high catalyst level is what gives rise to the very rapid cure out of the polymers in accordance with the present invention.
The polyisocyanurates are characterized by higher percent trimer content than prior art polymers. Unexpectedly, this higher trimer level is reached at lower peak reaction exotherm levels compared to the prior art polymers.
In a further advantage to flow from the present invention, there is superior processing latitude in the present polymers compared to the prior art materials.